Currently, as of 16.2.2, there is an option to do a backup of the undercloud database using the option "openstack undercloud backup --db-only". We want also to have this same functionality for overcloud database, so we could take a database backup of one of the nodes of the galera database by using the option "openstack overcloud backup --db-only".
*** Bug 2121385 has been marked as a duplicate of this bug. ***
The references to "openstack overcloud backup --db-only" was an error in documentation which has since been corrected. The preferred method of backing up the overcloud is the already existing procedure which backs everything up. The backup of only the database has very limited value, and is not high enough on our priority list to formally test and support.